<body>
    <style>
        h1{
            color:red;
            font-size: 18px;
        }
        #hi{
            color:seagreen;
        
        }
        .hello{
            color:rgb(20,50,100)
        }
    </style>
    <h1>你好啊😊</h1>
    <h1 id="hi">你好啊😊</h1>
    <h1 class="hello">你好啊😊</h1>
</body>